Bottom Line:
Another hormonal gene, Oxt, was up-regulated induced by stress in wild-type and Per2 mutant but not in Per1 mutant.In addition, the stress significantly elevated the serum corticosterone levels without genotype-dependent differences, and accordingly the glucocorticoid receptor gene, Nr3c1, expressed with a similar pattern in PVN of all strains.Therefore, our findings suggest a novel functional role of Per1 in neuroendocrine stress system, which further participates in analgesic regulation.

ABSTRACTAcute stressors induce changes in numerous behavioral parameters through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Several important hormones in paraventricular nucleus of the hypothalamus (PVN) play the roles in these stress-induced reactions. Corticotropin-releasing hormone (CRH), arginine-vasopressin (AVP) and corticosterone are considered as molecular markers for stress-induced grooming behavior. Oxytocin in PVN is an essential modulator for stress-induced antinociception. The clock gene, Per1, has been identified as an effecter response to the acute stresses, but its function in neuroendocrine stress systems remains unclear. In the present study we observed the alterations in grooming and nociceptive behaviors induced by acute immobilization stress in Per1 mutant mice and other genotypes (wild types and Per2 mutant). The results displayed that stress elicited a more robust effect on grooming behavior in Per1 mutant mice than in other genotypes. Subsequently, the obvious stress-induced antinociception was observed in the wild-type and Per2 mutant mice, however, in Per1 mutant, this antinociceptive effects were partially-reversed (mechanical sensitivity), or over-reversed to hyperalgesia (thermal sensitivity). The real-time qPCR results showed that in PVN, there were stress-induced up-regulations of Crh, Avp and c-fos in all of genotypes; moreover, the expression change of Crh in Per1 mutant mice was much larger than in others. Another hormonal gene, Oxt, was up-regulated induced by stress in wild-type and Per2 mutant but not in Per1 mutant. In addition, the stress significantly elevated the serum corticosterone levels without genotype-dependent differences, and accordingly the glucocorticoid receptor gene, Nr3c1, expressed with a similar pattern in PVN of all strains. Taken together, the present study indicated that in acute stress treated Per1 mutant mice, there are abnormal hormonal responses in PVN, correlating with the aberrant performance of stress-induced behaviors. Therefore, our findings suggest a novel functional role of Per1 in neuroendocrine stress system, which further participates in analgesic regulation.

pone-0016212-g002: Acute nociception and its change responses to immobilization stress in different genotypes.(A) The withdrawal response to von Frey filament stimuli. (B) The withdrawal latency to thermal stimuli (hot-plate, 55°C). Box plot graphs represent the distribution of values in the behavioral responses. The details referred to legends in Figure 1. In thermal withdrawal latency, the differences in mean response levels between the Per1 mutant (Per1 M; 9.28 sec), the Per2 mutant (Per2 M; 6.27 sec) and the mixed back-ground wild-type mice (M-WT; 7.34 sec) were statistically significant: *, p<0.05; **, p<0.01; ***, p<0.001, one way ANOVA. The change-fold of the withdrawal response to von Frey filament stimuli and the withdrawal latency to thermal stimuli are shown in (C) and (D), respectively. The asterisks (*, p<0.05; **, p<0.01; ***, p<0.001, one way ANOVA) indicate in each genotype, the significant differences in the behavioral responses of the stressed mice compared to the non-stressed mice, which is designated as 1. # indicate the significant differences of change-fold in behavioral responses between different genotypes (#, p<0.05; ##, p<0.01; ###, p<0.001, One way ANOVA).

pone-0016212-g002: Acute nociception and its change responses to immobilization stress in different genotypes.(A) The withdrawal response to von Frey filament stimuli. (B) The withdrawal latency to thermal stimuli (hot-plate, 55°C). Box plot graphs represent the distribution of values in the behavioral responses. The details referred to legends in Figure 1. In thermal withdrawal latency, the differences in mean response levels between the Per1 mutant (Per1 M; 9.28 sec), the Per2 mutant (Per2 M; 6.27 sec) and the mixed back-ground wild-type mice (M-WT; 7.34 sec) were statistically significant: *, p<0.05; **, p<0.01; ***, p<0.001, one way ANOVA. The change-fold of the withdrawal response to von Frey filament stimuli and the withdrawal latency to thermal stimuli are shown in (C) and (D), respectively. The asterisks (*, p<0.05; **, p<0.01; ***, p<0.001, one way ANOVA) indicate in each genotype, the significant differences in the behavioral responses of the stressed mice compared to the non-stressed mice, which is designated as 1. # indicate the significant differences of change-fold in behavioral responses between different genotypes (#, p<0.05; ##, p<0.01; ###, p<0.001, One way ANOVA).

Bottom Line:
Another hormonal gene, Oxt, was up-regulated induced by stress in wild-type and Per2 mutant but not in Per1 mutant.In addition, the stress significantly elevated the serum corticosterone levels without genotype-dependent differences, and accordingly the glucocorticoid receptor gene, Nr3c1, expressed with a similar pattern in PVN of all strains.Therefore, our findings suggest a novel functional role of Per1 in neuroendocrine stress system, which further participates in analgesic regulation.

ABSTRACTAcute stressors induce changes in numerous behavioral parameters through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Several important hormones in paraventricular nucleus of the hypothalamus (PVN) play the roles in these stress-induced reactions. Corticotropin-releasing hormone (CRH), arginine-vasopressin (AVP) and corticosterone are considered as molecular markers for stress-induced grooming behavior. Oxytocin in PVN is an essential modulator for stress-induced antinociception. The clock gene, Per1, has been identified as an effecter response to the acute stresses, but its function in neuroendocrine stress systems remains unclear. In the present study we observed the alterations in grooming and nociceptive behaviors induced by acute immobilization stress in Per1 mutant mice and other genotypes (wild types and Per2 mutant). The results displayed that stress elicited a more robust effect on grooming behavior in Per1 mutant mice than in other genotypes. Subsequently, the obvious stress-induced antinociception was observed in the wild-type and Per2 mutant mice, however, in Per1 mutant, this antinociceptive effects were partially-reversed (mechanical sensitivity), or over-reversed to hyperalgesia (thermal sensitivity). The real-time qPCR results showed that in PVN, there were stress-induced up-regulations of Crh, Avp and c-fos in all of genotypes; moreover, the expression change of Crh in Per1 mutant mice was much larger than in others. Another hormonal gene, Oxt, was up-regulated induced by stress in wild-type and Per2 mutant but not in Per1 mutant. In addition, the stress significantly elevated the serum corticosterone levels without genotype-dependent differences, and accordingly the glucocorticoid receptor gene, Nr3c1, expressed with a similar pattern in PVN of all strains. Taken together, the present study indicated that in acute stress treated Per1 mutant mice, there are abnormal hormonal responses in PVN, correlating with the aberrant performance of stress-induced behaviors. Therefore, our findings suggest a novel functional role of Per1 in neuroendocrine stress system, which further participates in analgesic regulation.